Morphology, optical and catalytic properties of polyethyleneimine-stabilized Au nanoparticles

• Au nanoparticles were stabilized by <0.05% polyethyleneimine in H2O and ethanol.
• Size and aggregation state of Au particles depend strongly on PEI content.
• Au–PEI particles catalyze methylviologen reduction by S2−.
• Au–PEI particles act as a co-catalyst of photocatalytic water reduction by TiO2.

Stable colloidal solutions of gold in water and ethanol were produced in the presence of small amounts of linear polyethyleneimine (PEI). In aqueous solutions a lowering of PEI concentration from 0.05 wt% to 0.0063 wt% results in an increase of the average size of Au particles from 3–7 nm to 30−40 nm. In ethanol 5–10 nm Au particles were produced in the presence of 0.0063–0.05 wt% PEI. At 0.05 wt% PEI the Au particles retain individual character but a lowering of PEI content to 0.0063 wt% causes particle aggregation into 80–140 nm globules. The Au–PEI nanoparticles exhibit catalytic activity in reduction of methylviologen bication to cation-radical by sulfide-ions as well as a co-catalyst of photocatalytic water reduction by ethanol with the participation of mesoporous TiO2. In both cases individual 4−8-nm Au–PEI particles show a much higher catalytic activity than 80−140-nm globules of aggregated Au–PEI NPs synthesized at a lower PEI content.

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